Long-Term Halogen Measurements at Cape Verde

Transcription

1 Long-Term Halogen Measurements at Cape Verde Ulrich Platt, Udo Frieß, Jessica Balbo Institut for Environmental Physics, University of Heidelberg, Germany Reactive Halogen Species in the Troposphere Previous Work of IUP Heidelberg DOAS and MAX-DOAS Expectations and Plans University of Heidelberg Institute for Environmental Physics

2 Reactive Halogens in the Atmosphere Stratosphere: Known since Lovelock, Global Strat. Ozone Depletion, Ozone Hole,... Sources: Longe lived organo-halogens Stratospheric Ozone destruction I Cl + O 3 ClO + O 2 ClO + O Cl + O 2 II Cl + O 3 ClO + O 2 Br + O 3 BrO + O 2 ClO + BrO Cl + Br + O 2 III ClO + ClO Cl 2 O 2 Cl 2 O 2 + hν Cl 2 + O 2 Troposphere: Known only since late 1980ies,... Sources: Short lived organohalogens, Sea salt, Volcanoes,... Consequences Ozone destruction, Reduction of Ozone formation, Modification of oxidation capacity Br (ng m -3 ), O 3 (ppbv) O3 Br Barrie et al April 1986

3 Simplified Outline of the Tropospheric XO X -Cycles XO X = X + XO Primary Emission (Algae, etc.) CH 3 X CHX 3 CH 2 X 2 etc. OH, hν X = I, Br, Cl HX RH,HO 2 OH XNO 2 X YO hν O 3, NO 2 XO NO 2 hν, hν YO hν hν HO 2 hν, HOX OXO XY, X 2 [ ] [ X] XO 1000 X = Cl, ( ) ( ) ( ) 100 X= Br, 10 X= I XONO 2 X 2 O 2 N 2 O 5 HX XONO 2 X 2 O 2 HOX Y - H + + X - Sea-Salt (Snow Pack or Aerosol)

4 Halogen Catalysed Destruction of Tropospheric O 3 Homogeneous reactions 1) XO + XO X + X + O 2 (rate determining) X 2 + O 2 X 2 + hν X + X 2 (X + O 3 XO + O 2 ) net: 2 O 3 3 O 2 2) XO + YO X + Y + O 2 (rate determining) XY + O 2 XY + hν X + Y ( Y + OXO + O 2 ) 2 nd order in RHS X + O 3 XO + O 2 Y + O 3 YO + O 2 net: 2 O 3 3 O 2 3) XO + HO 2 HOX + O 2 (rate determining) HOX + hν X + OH OH + AO HO 2 + A (AO = O 3, CO,...) net: 2 O 3 3 O 2 1 st order in RHS

5 Impediment of NO X and HO X Catalysed Tropospheric Ozone Production by Halogen Oxides XO + HO 2 HOX+O 2 HOX + hν OH + X XO XO + NO NO 2 + X X + O 3 XO + O 2 The product: [HO 2 ]x[no] and thus the rate of O 3 formation is reduced XO

6 Tropospheric Halogen Domains From: v. Glasow & Platt, HitT Description

7 IO Precursor: CH 2 I 2 or I 2? Data from Mace Head 1998, and Brittany, France, 2003 CH 2 I 2 [ppt] Date photopic [klx] IO concentration [ppt] 2 Jun 3 Jun 4 Jun 5 Jun 6 Jun 7 Jun Tidenhöhe [m] TH [m] Jun 3 Jun 4 Jun 5 Jun 6 Jun 7 Jun Date IO at Lilia, Brittany, France, Atlantic Coast , C. Peters et al CH 2 I 2 by Lucy Carpenter, taken from Kai Hebestreit Ph. D. Thesis, Univ. of Heidelberg, 2001

8 DOAS Measurements of I 2 at Mace Head, Oct Data from Hönninger et al., re-evaluation by C. Peters Molecular Iodine is only seen at very low tide Forest of Laminaria Digitata

9 I 2, IO, OIO, and BrO during NAMBLEX at Mace Head, 2002 Saiz-Lopez et al., ACP 6, 2006 BrO at August 3, 4, 10 of 2002

10 Summary: Consequences of RHS in the Troposphere Catalytic destruction of ozone Reduction of the HO 2 /OH ratio XO Enhancement of the NO 2 /NO ratio Potentially strong influence on the global tropospheric ozone budget XO Change of oxidation capacity (e.g. reduction of DMS) Primary particle formation (IO X ) Particle formation: [Hoffmann et al. 2001, Jimenez et al. 2003, Burkholder et al. 2004]: Precursor (org. or I 2 ) + hν I + I + O 3 IO + O 2 IO + IO OIO + I OIO + OIO I 2 O 4 + O 2 I 2 O 4 + OIO particle

11 Preceding Work of our Laboratory Related to RHS in General Our Group has been involved in Investiations of most experimental aspects of tropospheric RHS including: Studies in polar regions (first identification of BrO in the Arctic and Antarctic Boundary Layers) Studies at Salt Lakes (first identification of BrO and IO at the Dead Sea and at the Salar de Uyuni) Studies in the free troposphere (first direct determination of BrO in the free troposphere by ballon-based spectroscopy) Studies at volcanoes (first identification of BrO, ClO, and OClO in volcanic plumes) Studies in coastal regions (first identification of IO in a coastal region (Mace Head, Ireland)) Satellite Studies (first measurement of polar trop. BrO from satellite) Identification of the Bromine Explosion Mechanism in polar regions. University of Heidelberg Institute for Environmental Physics

12 Intensität Intensity ( ) [cm 2 ] Differential Optical Absorption Spectroscopy (DOAS) The Idea a b I 0 D' ' b [nm] I' 0 Use differences of intensities at different wavelengths Record the intensity in many (typ. several 100) wavelength channels (entire spectra) High pass-filtering of spectra remove continuum Fit reference spectra Make use of all spectral information Cross Sections [arb.units] BrO IO I 2 OIO Cabo Verde Spectrometer: BrO, IO, NO 2, CH 2 O wavelength [nm]

13 ϑ = 80 Stratospheric Layer MAX-DOAS The Idea ϑ AMF= SCD VCD ϑ = 30 Stratosphere: Signal determined by Solar Zenith Angleϑ AMF strat = AMF(ϑ) Boundary Layer: Signal determined by Observation Elevation Angle α AMF BL = AMF (α ) Boundary Layer O Observer Mean free path (355nm)=8-10km α Total Slant Column: S = S Trop 1 + S sinα Strat 1 = V cosϑ a 1 sin + α 1 cosϑ ( 1 a) Hönninger, v. Friedeburg, and Platt, Atmos. Chem. Phys. 4, , 2004

14 The Mini MAX-DOAS Instrument Cabo Verde Spectrometer: BrO, IO, NO 2, CH 2 O Copper Block Thermal Insulation Peltier Element Cooling Fins Miniature Spectrometer (Ocean Optics USB 2000) Telescop e Optical Fiber (also scrambles polarisation) Lens PC-Board (Electronics)

15 MAX - DOAS on the Atlantic (Polarstern, 2000) Time of day, October 1 Englisch Channel Time of day, October 12 Mid Atlantic Leser et al., GRL 2003 doi: /2002gl015811

16 Radiation Transport Considerations for MAX-DOAS Measurements Zenith direct sunlight Radiation scattered into the spectrometer's field of view Weighting Function α Shallow trace gas layer: Strong increase of trace gas column density with decreasing observation elevation angle Deep trace gas layer: Little increase of trace gas column density with decreasing observation elevation angle Spectrometer Spectrometer Spectrometer

17 Vertical Resolution of MAX-DOAS --> Poor Man s LIDAR SCD s Measured on May 4, 2000 (15:15 UT 15:40 UT), Alert 2000 PSE α -1 [deg -1 ] SCD BrO [10 14 cm -2 ] measured modelled P1 (0-1km) P2 (0-2km) P3 (0-1km+1-2km) P4 (1-2km) P5 (O 4 ) P6 (strat.) elevation angle α [ ] Hönninger and Platt, Atmos. Environ. 36, 2481,

18 Also Measure Species with Known Abundance, e.g. O 4 Aerosol Optical Density and Layer Height from O 4 Sinreich et al., Faraday Discuss. 130, , DOI: /B419274P, 2005 Intensity

19 dscd 1.50E E E E E+014 BrO at Cape Verde, Oct , E E /10/ /10/ /10/ /10/ /11/ E+015 BrO Date 1.00E E+014 Spectral Range: nm NO 2, BrO, IO (CH 2 O) dscd 6.00E E E E E :00 04:48 09:36 14:24 19:12 24:00 Time

20 dscd 1.00E E E E+016 NO 2 at Cape Verde, Oct , E E E /10/ /10/ /10/2006 Date 31/10/ /11/ E E+016 dscd 4.00E E E :12 09:36 12:00 14:24 16:48 19:12 Time

21 Questions, Hopes, and Plans... Scientific Questions: What is the liberation mechanisms of reactive halogen species from aerosol (and sea water?)? What is the role of Biogenic Sources and the transformation of organo-halogen species? What is the role of dust on halogen cycling? What is the extend of particle formation from halogen (iodine) precursors? What are the possible consequences global change on halogen and other chemistry? What are the consequences of tropospheric halogen chemistry on the oxidation capacity of the atmosphere and its impact on climate? Observations, e.g. BrO, IO dust correlations BrO, IO correlations with organohalogen levels BrO, IO correlations with biological activity in the ocean Future Better spectrometer (include I 2, OIO) Dedicated aerosol spectrometer...